title: Chiral plasmonic nanostructures on achiral nanopillars.
abstract: Chirality of plasmonic films can be strongly enhanced by three-dimensional (3D) out-of-plane geometries. The complexity of lithographic methods currently used to produce such structures and other methods utilizing chiral templates impose limitations on spectral windows of chiroptical effects, the size of substrates, and hence, further research on chiral plasmonics. Here we demonstrate 3D chiral plasmonic nanostructures (CPNs) with high optical activity in the visible spectral range based on initially achiral nanopillars from ZnO. We made asymmetric gold nanoshells on the nanopillars by vacuum evaporation at different inclination and rotation angles to achieve controlled symmetry breaking and obtained both left- and right-rotating isomers. The attribution of chiral optical effects to monolithic enantiomers made in this process was confirmed by theoretical calculations based on their geometry established from scanning electron microscope (SEM) images. The chirality of the nanoshells is retained upon the release from the substrate into a stable dispersion. Deviation of the incident angle of light from normal results in increase of polarization rotation and chiral g-factor as high as -0.3. This general approach for preparation of abiological nanoscale chiral materials can be extended to other out-of plane 3D nanostructures. The large area films made on achiral nanopillars are convenient for sensors, optical devices, and catalysis.
authors.affiliation: Departments of Chemical Engineering, University of Michigan , Ann Arbor, Michigan 48109, United States.
authors.forename: Bongjun
authors.initials: B
authors.lastname: Yeom
authors.forename: Huanan
authors.initials: H
authors.lastname: Zhang
authors.forename: Hui
authors.initials: H
authors.lastname: Zhang
authors.forename: Jai Il
authors.initials: JI
authors.lastname: Park
authors.forename: Kyoungwon
authors.initials: K
authors.lastname: Kim
authors.forename: Alexander O
authors.initials: AO
authors.lastname: Govorov
authors.forename: Nicholas A
authors.initials: NA
authors.lastname: Kotov